Photosynthetic Generation of O₂ and H₂ by Photosystem I-Deficient Chlamydomonas Mutants

V. A. Boichenko

Institute of Soil Science and Photosynthesis, Russian Academy of Sciences, Pushchino, Moscow Region, 142292 Russia; fax: (0967) 79-0532; E-mail: boich@ibpm.serpukhov.su

Received May 14, 1997; Revision received October 20, 1997

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A comparative study of aerobic generation of O₂ and anaerobic photoproduction of H₂ in whole cells of a wild-type strain of Chlamydomonas reinhardtii and its photosystem I-deficient mutants B4 and F8 found no contribution of photosystem II to ferredoxin photoreduction, which is not consistent with data of recent studies by Greenbaum et al. (Nature, 1995, 376, 438-441; and Science, 1996, 273, 364-367) who reported that they had discovered such a capacity in these mutant strains. In the wild-type and mutant strains, action spectra showed that O₂ was evolved by photosystem II, whereas photoinhibition of chlororespiration and evolution of H₂ depended on the activity of photosystem I. Single-turnover flash measurements of H₂ evolution showed that the contents of photosystem I in mutant strains amounted to 3-35% of that in the wild-type strain. This fraction of photosystem I in "leaky" mutants displayed abnormal kinetic features and was highly sensitive to photoinhibition.

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KEY WORDS: Z-scheme of photosynthesis, mutants, photosystem I, photosystem II, electron transport, ferredoxin, O₂ evolution, photoinhibition of chlororespiration, photoproduction of H₂

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